Spark-plug tool



March 19, 1940. c. A. SCHULZ I 2,193,886

I SPARK-PLUG TO OL Filed Feb. 17, 1938 INVENTOR ATTORNEY i atented Mar.19,1940 I PATENT oFFicE SPARK-PLUG TOOL Christopher A. Schulz,Guttenberg, N. L, as-

signor to The B. G. Corporation, New York,

N. Y., a corporation of New York Application February 17, 1938, SerialNo. 190,953

3 Claims.

A highly successful type of spark plug widely used in aviation enginesincludes a center electrode that has a concave surface at its lower end,and a shell surrounding the center electrode with a complementary innerface, preferably in the form of wide prongs, uniformly spaced from thecenter electrode surface. The spark jumps between the center electrodeand the wide-prongs, the point of discharge. shifting fitfully acrossthe spaced complementary surfaces.

When any points on these discharge surfaces become pitted or worn away,the spark jumps between other points that remain at the correct spacing.An extremely long term of service-is required before the large surfacesbetween which the sparkcan jump become worn over-sufficient area tointerfere with the operation of the plug. Such spark plugs give long andreliable service under severe engine conditions. When it does finallybecome necessary to adjust the spacing of the electrode surfaces,however, the adjustment must be made with great accuracy and it isimportant that the part of the shell electrode that has thecomplementary discharge surface spaced from the center electrode beformed to a truly complementary shape. The reforming of the shellelectrode is a part of the adjustment of the spark plug.

It is an object of this invention to provide improved apparatus forforming the electrode surface of the shell and effecting correct spacingof the discharge surfaces in a spark plug of the character indicated. Amore specific object of the invention is to provide a single tool withwhich the different operations of forming and adjusting the electrodesurfaces can be efficient-- ly carried out.

plugs that have been in service for a long period. Other objects,features and advantages of the invention will appear or be pointed outas the specification proceeds.

In the accompanying drawing, forming a part hereof:

Fig. 1 is a front elevation of a tool embodying this invention and shownwith the plunger against a spark plug shell for forming the elecdo- Fig.4.

This invention is used both for manufacturing spark plugs and forreconditioning.

The embodiment of the invention shown .in the drawing has a frame Illwith countersunk screw holes I I through its base for anchoring theframe to a work bench if a permanent location for the tool is desired.

A circular bar has gear teeth out in one side to form a rack. This barwill be referred to hereinafter as the rack bar i3. There is a verticalbearing M in the frame it, and the rack bar it slides up and down inthat bearing. A horizontal shaft ll turns in bearings in the frame Illand has gear teeth out in it to form a pinion II that engages the rackII. The shaft i1 is turned by a hand-wheel l9 that is rigidly secured toone end of the shaft.

The hub of the hand-wheel l9 contacts with a boss on the side oftheframe l0, and the shaft I1 is just long enough to extend through itsbearing in the frame. A washer is held against the end of the shaft Itby, a screw 2| that threads into the end of the shaft. The washer 20contacts with a boss on the sideof the frame to prevent displacement ofthe shaft H to the right,

-- in Fig. l, and the hub of the hand-wheel i8 prevents displacement ofthe shaft l1 toward the left. For the use of left-handed operators, how--ever, the screw 2i and washer 20 can be removed and the shaft I! pulledout of its bearings and inserted from the left side of the frame.

The rack bar l3 has a tapered lower end in which is a socket 23. Thebottom of the rack bar is formed into a die, which is indicatedgenerally bythe reference character 25. Thus the bottom end of the rackbar is itself a tool in the illustrated embodiment of the invention, butthe die can be a separate piece and attached to the lower end of therack bar.

0n the base of the frame It there is a carriage guldeway including asupporting surface 27 with guide surfaces 28 extending'along both thefront and back edges of the surface 21.

A die 30, which is shaped for the-particular spark plug sleeve that is.to be formed, has a stem 3| that fitsinto a socket 32 in the base of theframe and in line with the rack bar i3. A hardened insert 3! in thesurface 21 at the upper end of the socket 32 prevents the surface frombeing scratched or nicked by the die or the shoulder of the die thatrests on the insert 36.

A spark-plug shell 35 fits over the die 30, and

the upper end of the die is substantially the shape desired for thedischarge surface of the shell.

The actual dimensions of the die 30 are a little oversize so that theprongs 31 at the end of the shell 36 are'spaced a few thousandthstoo farapart and can be bent into exact positionas determined by a thicknessgauge.

The rack bar is lowered until the die 25 is in contact with the shell.The rack bar is .then struck on the top with a hammer once or twice tobend the prongs at the end of the shell to the exact contour of the die.The die 25 at the bottom of the rack bar I3 is shaped so that it has adrawing action over the die 30 rather than a true forming action asunderstood in the die art. The operation is referred to herein as theforming of the shell, however, using the term in its broader sense.

The die 30 is held in position by a die lock pin 38 clamped against thestem 3| by a set-screw 39 threading through the forward wall of thebase.

After the forming of the shell 36 in the manner described above, theshell 36 is screwed onto the rest of the plug 4|, as shown in Fig. 4,and the assembled spark plug is inserted through a bushing 43 andthreaded into a face plate 44 of a carriage 45 until the shoulder 41 ofthe plug comes against the end of the bushing 43.

The carriage 45 rests on the supporting surface 21 and has a widthsubstantially equal to the distance between the guide surfaces 28, bestshown in Fig. 2. When the carriage has been moved into position tolocate the electrode end of the plug in the proper relation to the pathof movement of the rack bar l3,-a set-screw 50, threaded into the frontof the frame I 0, is tightened against the carriage 45 to lock it inposition.

The carriage 45 includes a body portion 52, a part of which extendsupward at a substantial acute angle to the vertical as shown in Fig. 4.The face plate 44 has a sleeve 53 extending from its back face. Thissleeve 53 fits into the upstanding part of the carriage body 52, and isheld in the carriage body by a set-screw 54, that extends into acircumferential groove 55 in the sleeve 53 9.nd leaves the sleeve andthe face plate 44 free to rotate.

The bushing 43 surrounds the tops of the outside threads of the shell 36and limits the extent to which the spark plug can be screwed into theface plate 44 by providing an abutment against which the shoulder of thespark plug strikes. The bushing 43 has a circumferential grooveregistering with a groove on the inside surface of the sleeve 53, and aspring 59 confined in these grooves holds the bushing againstdisplacement from the sleeve. The spring 59 yields, however,-to permitthe bushing to be forced from the sleeve when a longer bushing is to beinserted for a different model of spark plug.

An electrode adjusting foot 6| has an enlarged upper end that fitssnugly into the socket 23 in the bottom of the rack bar 13. Theadjusting foot 6| is held fast in the socket by a set-screw 62 (Figs. 1and 2), and the rack and pinion mechanism is operated to bring theadjusting foot down against the uppermost prong 3'! of the spark-plugshell 35. A thickness gauge 64 is inserted between the center electrodeof the spark plug and the uppermost prong 31 of the shell; thehand-wheel is then operated, and the prong is pressed against thethickness gauge with sufllcient force to reduce the clearance betweenthe electrode surfaces to the dimension of the thickness Y gauge.

The face plate 44 is turned to bring each of the four prongs on the endof the shell 36 successively into position under the adjusting foot 6|.Fig. 3 illustrates the manner in which an operator holds the thicknessgauge 64 in' one hand and turns the hand-wheel IS with the other hand.The hand-wheel is of such a size in proportion to the size of the pinionand other parts that no injury to the plug will be caused with anyreasonable force that is applied to the hand-wheel.

The preferred embodiment of the invention has been illustrated anddescribed, but modifications can be made and some features of theinvention may be used without others.

, I claim:

1. A tool for spark plugs that have a center electrode with a curvedsurface, and a sleeve portion having one or more other electrodes eachwith a complementary surface that is uniformly spaced from the centerelectrode surface over a substan' tial area when the spark plug isassembled, said tool comprising a frame with means for engaging andholding said sleeve portion of a spark plug in a fixed position, a rackbar movable in a bearing in a portion of said frame toward and from anelectrode of a sleeve portion so held, and a die which is located at theend of the rack bar and which is so curved that it forms the electrodeof the sleeve portion on the engaging and holding means to saidcomplementary surface when said die on'the rack bar is pressed againstthe electrode with a deforming pressure.

2. A spark-plug tool for making the surface of an electrode on aspark-plug shell correspond to the curve of a complementary centerelectrode of the spark plug, said tool including a frame having a baseon which is a supporting surface, an upper frame portion with a bearing,a rack bar slidable in the bearing toward and from the supportingsurface on the base, a handle and pinion for causing the rack to move upand down, a socket in said supporting surface, die means comprising amember with a stem at the lower end that fits into the socket, an upperportion shaped to receive a spark-plug shell and a top surface thatforms a die with a surface of substantially the desired shape of thesurface of the electrode on the spark-plug shell, 9. second die thatcooperates with the die means on which the electrode shell is supported,said second die being formed at and integral with the lower end of therack bar and being of a curved shape to cooperate with the die on theshell-supporting die means to form the shell electrode surface to thedesired shape.

3. A tool for spark plugs of the type which have a shell with electrodeprongs that converge inward from the end of the shell and toward theaxis of the spark plug, said tool including a first die having a portionthat engages and holds the spark-plug shell in a definite position andhaving another portion with a tapering surface of substantially thedesired shape of one side of the converging electrode prongs, a seconddie having a tapering surface complementary to the tapering surface ofthe first die and constructed and arranged to compress the electrodeprongs against the die that receives the spark-plug shell, supportingmeans associated with the die that receives the spark-plug shell forholding that die and said shell in a definite position in the path ofsaid second die, and means connected in definite relation to the diesupporting means for forcing one of the dies against the other to com- 3press the electrode prongs between said dies.

CHRISTOPHER A. SCHULZ.

